Two senior GOP senators on Monday released a copy of their request for a criminal probe of Christopher Steele, the author of a controversial dossier on President Donald Trump’s ties to Russia, which alleges that he received information from an ally of Hillary Clinton while the Democrat’s campaign was financing his work.

Senate Judiciary Committee Chairman Chuck Grassley (R-Iowa) and Sen. Lindsey Graham (R-S.C.) released their referral for a Steele investigation, sent last month, after approval from the FBI.

Grassley and Graham on Monday also asked the Department of Justice and FBI to declassify more information related to their Steele referral, including an application to conduct surveillance of former Trump campaign adviser Carter Page.

That surveillance application, Republicans have said, improperly involved research conducted by Steele that was paid for by the Clinton campaign. Republicans on Friday released a declassified memo they wrote on the subject.

The referral document released Monday regarding Steele cites a second, unpublished research document prepared by Steele, based on material given to him by a source who received it from “a friend of the Clintons.”

“It is troubling enough that the Clinton campaign funded Mr. Steele’s work, but that these Clinton associates were contemporaneously feeding Mr. Steele allegations raises additional concerns about his credibility,” Grassley and Graham wrote in the Jan. 5 referral.

The unclassified referral also echoes concerns raised by House Intelligence Committee Republicans about Steele’s contact with reporters about his dossier, which alleges a Kremlin-backed plan to amass damaging material about Trump while helping his 2016 campaign. Steele has acknowledged meeting with reporters off the record in mid-2016 to discuss his work, the Republicans said.

“Simply put, the more people who contemporaneously knew that Mr. Steele was compiling his dossier, the more likely it was vulnerable to manipulation,” the senators wrote.

Other lawmakers have called for more information to be declassified surrounding the FBI’s surveillance of Page. Reps. Brad Wenstrup (R-Ohio) and Jim Himes (D-Conn.) both told CNN that they would support the release of the government’s application to monitor Page, whose ties to Russia reportedly first attracted the notice of law enforcement officials in 2013.

The Department of Justice had no comment on the Republican senators’ letter Monday.